Digital watermarking is a process for modifying physical or electronic media content to embed a hidden machine-readable code into the media. In digital watermarking, a media content signal, such as an image or audio signal, is modified to embed a hidden, digital auxiliary code signal such that the auxiliary signal is imperceptible or nearly imperceptible to the user, yet may be detected through an automated detection process. Most commonly, digital watermarking is applied to media content signals such as images, audio signals, and video signals. However, watermarking may also be applied to other types of media objects, including documents (e.g., through line, word or character shifting, through background patterns or tints, etc.), software, multi-dimensional graphics models, and surface textures of objects.
Digital watermarking systems typically have two primary components: an encoder that embeds the watermark in a host media signal, and a decoder that detects and reads the embedded watermark from a signal suspected of containing a watermark (a suspect signal). The encoder embeds a watermark by subtly altering the host media signal. The reading component analyzes a suspect signal to detect whether a watermark is present. In applications where the watermark encodes information, the reader extracts this information from the detected watermark.
Several particular watermarking techniques have been developed. The reader is presumed to be familiar with the literature in this field. Particular techniques for embedding and detecting imperceptible watermarks in media signals are detailed, e.g., in the assignee's co-pending U.S. patent application Ser. No. 09/503,881 and U.S. Pat. No. 6,122,403, which are each hereby incorporated by reference.
Another technology referred to as fingerprinting, in contrast to digital watermarking, does not embed auxiliary data in a media signal, but rather, derives a unique content signal identifier from the media signal itself. For some applications where the signal undergoes a transformation in normal use, such as compression, transmission, or digital to analog to digital conversion, the fingerprint (or host signal characteristics used to determined a fingerprint) preferably remains relatively unchanged, allowing unique identification of the content signal. Fingerprints for a wide selection of media signals may be stored in a database and associated with information or actions to be taken upon detection or calculation of a fingerprint.